As will be appreciated, numerous abnormal conditions may occur in flight that could lead to complete or partial failure of a jet aircraft's hydraulic system. For example, if one of the turbine engines should experience a catastrophic failure (e.g., rotor burst), turbine blade or blade fragments could be hurled into the fuselage causing extensive damage to the hydraulic system. Such damage could include disabling of the hydraulic pump, accumulator failure, and severing of hydraulic lines. Further, hydraulic lines, motors, pumps, and/or accumulators may fail during flight, and result in partial or complete failure of the hydraulic system.
To deal with such abnormal conditions, redundancy in the system is desired so that the various devices operated by the hydraulic system have an alternate source of operating pressure, at least sufficient to operate the devices through several cycles.
In larger jet aircraft, redundancy is achieved through the use of redundant hydraulic systems, including multiple pumps, multiple reservoirs and multiple fluid lines for each device to be operated. These complex redundant systems are effective but add weight to the aircraft and take up considerable space. Such systems are not practical for use in smaller jet aircraft.
Because smaller jet aircraft are relatively light, they can use purely mechanical linkages (e.g., cables, push-pull rods, etc.) for operating in-flight control devices such as ailerons, elevators, and rudders. Nevertheless, smaller jet aircraft typically require a power system or systems to operate devices that control landing gear extension and retraction, main landing gear wheel brakes, nose wheel steering and speed brake deployment and retraction, for example.
These circumstances necessitate a new type of hydraulic system that provides for continued operation of the direction and deceleration control devices in the event of an abnormal condition. Accordingly, a new approach for the hydraulic system is required so as to provide the redundancy necessary to assure safe operation in emergencies.